[SI-LIST] Re: EMC Issue at 266 MHz
- From: "npischl" <npischl@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 01 Mar 2004 18:43:57 -0000
I would say it is certain that is does come from your clock. You see
the 4th harmonic because even a slight deviation (<1%) from perfect
50% duty cycle results in strong even harmonics. In addition to the
signals that are not perfectly symmetrical, the other contribution
to emission may be (and probably is) related to power supply having
strong 66.66 MHz components due to di/dt of the clocks.
Neven
--- In si-list@xxxxxxxxxxxxxxx, Jean_Pierre.Bouthemy@xxxx wrote:
> Hi SI experts,
>
> I have a question regarding an EMC issue.
> Our system has failed the EMC radiated emissions with a 266.6 MHz
emission
> +3dB above Class A gabarit !
> We have many 66.66 MHz clocks in our system, made with 50MHz
oscillator
> feeding a PLL, whose 400 MHz VCO frequency divided by 6 gives
66.66 MHz.
> My question is the following:
> I could understand an emission at the odd harmonics:
> - 66.66MHz x 3 = 200 MHz or,
> - 66.66MHz x 5 = 333.33 MHz or,
> - 66.66 MHz x 7 = 466.66 MHz or,
> - so on ...
>
> But I don't understand why we have problem with the fourth
harmonic : 66.66
> MHz x 4 = 266.6 MHz !!
> => Does anyone have an idea ?
> => Is it possible the 266MHs emission doesn't come from our
66.66MHz
> clocks?
> => In this case wher could it be from?
>
> Thank you for your help.
> Regards.
>
> Jean-Pierre Bouthemy
>
>
> -------------------------------------------------------------------
-
> Jean-Pierre BOUTHEMY
> Hardware Design Engineer
> ALCATEL - Mobile Networking Division (MCG)
> Mobile Core R&D
> +33 (0)2 99 26 08 18
> mailto:jean_pierre.bouthemy@xxxx
> -------------------------------------------------------------------
-
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxx with 'help' in the Subject field
>
> List technical documents are available at:
> http://www.si-list.org
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
